keith



A. E. KEITH.

AUTOMATIC TELEPHONE SYSTEM.

ICATION nuzo AUG.3I, 1914. RENEWED APR Patented Nov. 18, l919.

4 SHEETSSHEET 1.

I WITNESSES HTTOR/VEKS,

A. E. KEH'H.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED AUG.31. I914. RENEWED APR-5,1919.

Patented Nov. 18, 191%.

4 SHEETSSHEET 2.

W/TA/ESSES A. E. KEITH.

AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED AUG.31, 1914. RENEWED APR. 5, 19:9.

knew/701?.-

177' TOP/VH5 JQEXH/YJEEDEEKEYTH W/T/VESSES A. E. KEITH.

AUTOMATIC TELEPHONE SYSTEM. APPLICATION FILED Aue.s1.1914. RENEWED APR.5, 1919. 1,322,025, Patented Nov. 18, 1919.

' 4 SHEETSSHEET 4.

w w E IMT/VESSES UNITED STATES PATENT OFFICE.

ALEXANDER E. KEITH, OF HINSDALE, ILLINOIS, ASSIGNOR T0 AUTOMATICELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Nov. 18, 1919.

Application filed August 31, 1914, Serial No. 859,439. Renewed April 5,1919. Serial No. 287,923.

To all whom it may concern:

Be it known that I, ALEXANDER E. KEITH, a citizen of the United Statesof America, and resident of Hinsdale, Dupage county, Illinois, haveinvented certain new and useful Improvements in Automatic TelephoneSystems, of which the following is a specification.

My invention relates to improvements in automatic telephone systems andmore particularly to systems employing selector and connector switchesfor establishing connection between tw lines.

Among the features or" my invention are the improved means forcontrolling the operation of the switches. Heretofore it has beencustomary for each switch to be provided with its own operatingmechanism. By my invention, however, I provide a common operatingmechanism which can be brought into operative relationship with any oneof a plurality of switches, and it is then automatically disconnectedtherefrom when the switch has been operated. In this manner theconstruction of the switches is greatly simplified and the total amountof apparatus necessary in an exchange greatly reduced.

In the acompanying drawings I have illustrated my invention inconnection with selector and connector switches of well-known types, andhave illustrated the common mechanism as associated only with theselector switches. This, however, is merely for the purpose ofillustration, as it will be readily apparent that the form of theswitches could be changed and that the common mechanism could beassociated equally as well with any of the other types of selectorswitches, or with the connector switches.

In the drawings Figure 1 is a diagrammatic layout of a telephone systemin which I have chosen to illustrate my invention.

Fig. 2 shows a side view of one of the selectors shown at F.

3 is a front view of the same switch.

Figs. i and 5 show a complete connection between two automaticsubstations in said system.

The telephone system illustrated in Fig. 1 comprises an automaticexchange or" the well-known type comprising subscribers individualpreselector or line switches C, so-

called first selector switches E, second selector switches F, controlswitches I and connector switches H. In the drawings there isrepresented on a scale of three to ten an exchange of ten thousand linescapacity. The subscribers substations and the lines connected theretoare divided into groups A A etc., of one hundred lines each. 011 a scaleof three to ten, therefore, the nine groups (A to A inclusive) representten thousand lines. With each group of subscribers lines there isassociated a group of individual or line switches C (one for each line),a group of first selectors E, a group of second selectors F and a groupof connectors H. Considering the groups A A and A as representing onethousand lines in the ten thousand line office, it will beseen thatthere is a group of control switches I associated with each thousandlines. The selector and connector switches comprise ianks of contactsarranged in horizontal rows or levels. These levels are representeddiagrannnatically by horizontal lines, which, in the case of the firstselectors E and the connectors H, extend across a group of switches,thereby indicating that the corresponding contacts of all the switchesof the groups are multipled together. In the case of the secondselectors F the banks are shown in a different manner, but it is to beunderstood that the bank contacts are multipled in the same manner asdescribed for the first selectors E and the connectors II. All of theline switches C belonging to a single group of subscribers lines havecommon access to a group of first selectors E. The correspondingcontacts of all the first selectors of the corresponding hundred in eachthousand are multipled together. Trunk lines leading from the firstlevel of the first selectors of the first hundred of each thousandextend to the group of second selectors associated with the firsthundred in the first thousand. Trunk lines leading from the second levelof the first hundred of each thousand extend to second selectorsassociated with the first hundred in the second thousand, etc. Thecorresponding bank contacts of all the second selectors in each thousandare also multipled together. Trunk lines leading from the first level ofthe second selectors of any thousand extend to connectors associatedwith the first hundred of that thousand. Trunk lines leading from thesecond level of the second selectors of any thousand extend toconnectors associated with the second hundred of that thousand, etc.This trunking arrangement of an automatic system is in general wellknown in the art and it is not thought necessary to describe it ingreater detail herein. The control switch I is equipped with a shaftwhich operates the wipers of a number of second selectors F. The systemis so arranged that this number consists of one second selector in eachhundred of the thousand with which the control switch I is associated.l/Vhen connection is made with one of the above-mentioned secondselector switches, the said second selector switch grips the commonshaft, and at the same time the other second selector switchesassociated with that particular control switch are made busy. Thereupon.the control switch operates to advance the wipers of th said secondselector to an idle contact in the called level, whereupon the wipers ofthe said second selector are released from the common shaft. The controlswitch then returns to normal and removes the guarding potential fromthe re maining second selectors associated therewith.

The automatic substation A (Fig. 4) comprises the usual receiver 2,transmitter 3, ringer 4 and condenser 5. Being an auto matic substationit is also provided with a suitable call-sending mechanism forcontrolling the automatic switches, which mechanism is representeddiagrammatically by a pair of impulse springs 6 and 7 and an impulsewheel 8, which latter may be controlled by a dial provided with fingerholes in such a way that the impulse springs may be momentarilyseparated a number of times corresponding to the respective digits ofthe number of the called subscriber.

The subscribers individual switch C (Fig. 4) is of the general type ofsubscribers switch shown in British patent to R. l/V. James No. 26,301of 1906, being, 110wever, of the particular type disclosed in Britishpatent to T. G. Martin No. 1419 of '1910. This line switch comprisesamong other details a plunger (not shown) attached to the end of aso-called plunger arm 9 which is controlled by the magnet 10. The magnet10 comprises four windings, namely, a pull-down winding 11, a cut-off orholding winding 12, a line winding 13 and an auxiliary winding 14. Thecore of the magnet 10 is so constructed that the magnetic circuit of thewindings 11 and 12 is separate from that of the windings 13 and '14.This magnet also controls the cutoff armature 15. The pull-in winding 11operates both the plunger arm 9 and the armature 15, while the cut-offor holding winding 12 is strong enough only to operate the cut-offarmature 15 and to hold the plunger arm 9 in its operated position. Whenthe plunger arm is operated, the

-plunger is forced into a bank of contact springs, forcing the springs16, 17, 18 and 19 into engagement with the springs 20, 21, 22 and 23,respectii ely. Although only one set of springs (16 to 23, inclusive) isshown, each line switch is provided with a plurality of such sets, eachset forming the terminal of a trunk line leading to a selector switch.Each trunk line is connected in multiple with the corresponding springsof all the line switches of the group which is controlled by the masterswitch D. The switch C is controlled by the subscriber through themedium of the line relay 13, as will hereinafter be more fullyexplained.

The master switch D (Fig. 4) is of the same general type as thatdisclosed in British patent to R. W. James No. 26,301 of 1906, being,however, of the particular type disclosed in British patent to T. G.Martin No. 1419 of 1910. The function of the master switch, as is wellknown, is to maintain the plunger-s of all the idle line switches inposition to engage the terminal of an idle trunk line.

The selector switch E (Fig. 4) is of the general type of selector switchdisclosed in United States Letters Patent No. 815,321, granted March 13,1906, to Keith, Erickson and Erickson, except that the so-called sidesWitch is omitted and the circuits are modified to adapt the switch tooperate in a system in which the central office apparatus is controlledby impulses delivered over the two sides of the line in series, as shownin British patent to T. G. Martin No. 10,376 of 1913. Among otherdetails the selector E comprises a bank of contacts arranged inhorizontal rows or levels, which contacts are adapted to be engaged by aset of wipers 24, 25 and 26 carried upon a shaft (not shown) which has avertical movement controlled by the vertical magnet 27 and a rotarymovement controlled by the rotary magnet 28. The operations of thevarious parts of the switch are controlled through the medium of thedouble-wound relay 29. Means for permitting the switch to be restored tonormal position are provided in the release magnet 30, which, uponenergizing, withdraws the retaining pawls from the shaft. The springs 31and 32 close only when the switch shaft has been raised one or moresteps from its lowest position. The relays 33 and 34 are slow actingthatis, they are slow to release their armatures upon deenergizing.

The control switch I (Fig. 4) is similar to the switch E except that ithas neither a bank of contacts or shaft wipers and its shaft (not shown)is of sufficient length to extend through ten of the so-called secondselector switches. The springs break contact only when the switch hasrotated one or more steps from normal position.

The second selector switch F (Fig. 4) is also similar to the switch Eexcept that its shaft 36 (Fig. 2) is hollow, thus allowing the shaft 370f thecontrol switch I to pass loosely through its center. At 38 and 39are shown two solenoids, which, when the switch is at normal, are soplaced that the combined effort of the two will cause the pin 40 (Fig.2) to be forced through the hole 41 in the shaft 36 into the hole 42 inthe shaft 37. Thus the shafts 36 and 37 will be locked together and anymotion of the shaft 37 will be transmitted to the shaft 36. The solenoid38 is of suficient strength to retain the pin 40 in an operated positiononce it has been operated. In Fig. 3 a projection on the shaft 36 isshown as resting upon the arm 43 and in this way keeping the springsshown at 44 in a normal position. Referring to Fig. 2, it will be seenthat the armature 45 of the relay 46 is extended in such a manner as tolock the arm 43 in a normal position even though the shaft 36 should beraised. With the shaft 36 raised one or more steps, the energization ofthe relay 46 unlocks the arm 43, which in turn allows the springs 44 toassume an operated position. At the release of the switch the shaft 36,upon reaching normal position, forces the arm 43 under the armature 45.The second selector switch F has neither vertical nor rotary magnets.The springs 135 make contact only when the switch has been rotated oneor more steps.

The connector switch H (lig. is of the same general type of connectorswitch disclosed in United States Letters Patent No. 815,176, grantedMarch 13, 1906, to K ith, Erickson and Erickson, the circuits, however,being modified to adapt the switch to operate in a system in which thecentral oilice apparatus is controlled by impulses delivered over thetwo sides of the line in series. Among other details the connector Hcomprises a bank of contacts arranged in horizontal rows or levels,which contacts are adapted to be engaged by a set of wipers 47, 48 and49 carried upon a shaft (not shown) which has a vertical movementcontrolled by the vertical magnet 50 and a rotary movement controlled bythe rotary magnet 51. The usual side switch comprises the wipers 52, 53,54 and 55 and is controlled by the private magnet 56 in the usual andwell-known manner. The operations of the various parts of the switch arecon trolled through the medium of the doublewound line relay 5?. Therelay 58 is the usual back-bridge relay through which the calledsubstation receives talking current. The ringing relay 59aifords meansby which ringing current is applied to the called line. Means forpermitting the switch to be re stored to normal position are provided inthe release magnet 169, which, upon energizing, withdraws the retainingpawls from the shaft. The springs 60 and 61 close only when the switchshaft has been raised one or more steps fron'i its lowest position. erelays and 63 are slow acting-that is, slow to release their armaturesupon deenergizing.

The called substation A and its individual switch 0 are similar in allrespect to the substation A and its individual switch (7.

For the purpose of supplying batter current for operating the apparatusand for talking there is shown the battery B having one terminalgrounded at G. For the purpose of supplying ringing current there isshown the ringing current generator it. The busy signaling machine Q, asrepresented herein, coinorises an induction. coil or transformer, theprimary winding of w 'ch is included in a local. circuit with a batteryand an interrupter. Through the medium of this interrupter anintermittent current is supplied to the primary winning. which inducesan alternating current in the secondary winding, whereby when saidwinding is connected with the subscribers lines a buzzing sound is heardin the receiver.

A. general description of the apparatus having been given, it will nowbe explained how a connection can be established ween the line ofsubstation A and the line of the called substation A. The number of thecalled substation will be assumed to be Since the automatic switchingapparatus disclosed herein is .in general. well known in the art, and isoescribed in the publications herein referred to, its opera ion will beor plained in a more or less general manner.

Then the subscriber at substation A removes the receiver 2 preparatoryto making a call, an energizing circuit is closed through the linewinding 13 of the line switch C. This circuit extends from ground Gthrough th springs 65 and 66, conductor 67 to and through the substationA, conductor 68, springs 69 and 70 and the line winding 13 to battery B.The armature 71, upon being operated, closes a circuit from ground Gthrough the springs 65 and 72, pull-in winding 11, auxiliary winding 14and the springs 7 3 to battery 13. The pull-in winding 11, uponenergizing, attracts both the armature 15 and the plunger arm 9. Theplunger arm 9, upon being attracted, forces the plunger which isattached to the end thereof into the bank of trunk terminals to which ithas access, forcing the springs 16, 17, 18 and 19 into engagement withthe springs 20, 21, 22 and 23, respectively. The engagement of thesprings 16 and 19 with the springs 20 and 23, respectively, closes acircuit through the line relay 29 of the first selector E. This circuitextends from ground G through the lower winding of the relay 29, springs74 and 75, springs 23 and 19, conductor (37 to and through thesubstation A, conductor 68, springs 16 and 20, springs 76 and 77 and theupper winding of the relay 29 to battery B. The relay 29, uponenergizing, closes a circuit as follows: from ground G through thesprings 78 and 79 and the relay 33 to battery B. The energization of therelay 33 closes a circuit extending from ground G through the springs80, springs 21 and 17 to the point 81, from which point one branchextends over the conductor 82 to the connector private bank contactassociated with the calling line and multiples of the same. Thisguarding potential prevents any party from connecting with thesubstation A when said substation is calling. Another branch extendsfrom the point 81 through the holding winding 12 to battery B. Thiscircuit through the holding winding 12 is closed before the armature 71falls back after the circuit through the line winding 13 is broken bythe attraction of the armature 15. The armature 71 does not fall backimmediately upon the pulling up of the armature 15, due to the fact thatsimultaneous with the attraction of the armature 15 is the pulling up ofthe plunger arm 9, which short-circuits the auxiliary winding 14 byclosing the springs 83. The short-circuiting of the winding 14 tends toretard the de'e' ner 'ization of the core and thus the armatureTl isheld in an operative position until enough time has elapsed for thecircuit through the winding 12 to be closed while the plunger arm 9 isheld in an operated position.

The calling subscriber now operates his calling device for the firstdigit 2 of the called number, whereby the substation impulse springs 6and 7 are separated twice momentarily, each time breaking the circuit ofthe lin relay 29 of the selector E. The relay 33 of the selector beingslow acting does not deenergize during the momentary interruptions ofits circuit by the relay 29, and consequently, each time the latterrelay denergizes, an impulse is transmitted over the circuit extendingfrom ground G through the springs 78 and 84, springs 85, springs 86 and87, relay 34: and the vertical magnet 27 to battery B. The verticalmagnet receives two impulses over this circuit and operates to raise theswitch shaft and wipers two steps to a position opposite the second rowor level of bank contacts, and at th same time the shaftcontrolledcontacts 31 and 32 are closed. The slow acting relay 34 is maintained inits energized position continuously while impulses are being transmittedto the vertical magnet therethrough, and in its energized positioncloses a circuit extending from ground G through the springs 88 and S9and the relay 90 to battery B. The relay 90, upon energizing, forms alocking circuit for itself extending from ground Gr at the relay 33through the springs 80, springs 91, off normal springs springs 92 and 93and the relay 90 to battery B. Thus, upon the de'oinergization of therelay 341- after the last impulse is delivered to the vertical magnet,the relay 90 remains energized and the circuit of the rotary magnet 28is closed, which circuit extends from ground G at the relay 33, springs80, springs 91, 011' normal springs 32, springs 92 and 93, springs 89and 94, springs and the rotary magnet 28 to battery B. The rotary magnet28, upon energizing, rotates the shaft wipers one step and, by openingthe springs 91 and 95, disconnects the ground G from itself and from therelay 90. If the first trunk line of the second level is idle, the relay90 deenergizes as soon as th springs 91 are opened. If this trunk lineis busy, however, the private wiper 25 finds the contact which itengages provided with a guarding ground potential which is transmittedto the relay 90 through the springs 92 and 93, and thereby, prevents itfrom deenergizing. The rotary magnet 28. however, de'e'nergizes when thesprings 95 are opened, regardless of whether the relay 90 remainsenergized or not. If the relay 90 remains energized, the circuit of therotary magnet will be again closed as soon as its armature drops backfar enough to close the springs 91 and 95. The rotary magnet willtherefore operate in a. manner similar to that of a buzzer to advancethe wipers step by step over the contacts, until the nongrounded contactof an idle trunk line is reached by the wiper 25, whereupon the relay 90deenergizes. The relay 90, upon deenergizing, whether after one orseveral operations of the rotary magnet, permanently breaks the circuitof said rotary magnet and closes the circuit of the switching relay 96.Said circuit extends from ground G* through the springs 80, springs 91,off normal springs 32, springs 92 and 97 and the relay 90 to battery B.The relay 96, upon energizing, disconnects the line relay 29 from theline and extends the line connection over the heavy conductors shownthrough the wipers 24: and 26 to the second selector F. A circuit maynow be traced from ground G through the upper winding of the relay 98,springs 99 and 100, wiper 26 to and through the substation A over thecircuit previously traced to the wiper 24:, springs 101 and 102, relay103, and the lower winding of the relay 98 to battery B. The relays 98and 103 energize over this circuit and the relay 103, upon energizing,completes a circuit from ground G through the springs 104, 105 and 106,private wiper 25, springs 92 and 97 and the relay 96 to battery B. Abranch of the above circuit may be traced from the private wiper 25through the off normal springs 32, springs 91 to the holding winding ofthe line switch C, over the circuit previously traced. This circuitmaintains the relay 96 and the winding 12 energized after their originalenergizing circuit is broken by the relay 33, which deenergizes shortlyafter the line relay disconnected from the line. A branch of theabovecircuit extends from th spring 106 through the springs107 and 108 to oneof the conductors 109, which extends to the private bank contactsassociated with each of the other idle selectors which are controlled bythe control switch I. As soon as the relay 103 of any selector isenergized, the remaining idle selectors in the group of which it forms apart are protected from being seized. Upon the energization of the relay103 another circuit is formed extending from ground G- through thesprings 104 and 105, solenoid 38 and solenoid 39 to battery B, whereuponthe solenoids 38 and 39 operate, as previously explained, to lock theshaft of the selector F with the shaft f the control switch I. Thesolenoid 39, upon energizing, closes a circuit from ground G through thesprings 112and 113 and the relay 114 to battery B. The relay 114, uponenergizing, prepares the circuit of the vertical magnet 115. It will beseen that when the solenoid 38 becomes energized, the resistance 111 andground G are placed in parallel with ground G the reason for which willbe hereinafter explained.

The calling subscriber now operates his calling device for the seconddigit 2 of the called number, whereby the substation inn pulse springs 6and 7 are separated twice momentarily, each time breaking the circuit ofthe line relay 98 of the control switch I. The relay 103 of the selectorF, which is included in the above circuit, being slow acting does notdenergize during the momentary interruptions of its circuit, andconsequently, each time the relay 98 deenergizes, an impulse istransmitted over the circuit extending from ground G through the springs116, springs 117 and 118, springs relay 119 and the vertical magnet 115to battery 13. The vertical magnet receives two impulses over thiscircuit and operates to raise the shaft 37, the shaft 36 and the wipers120, 121 and 122 two steps to a position opposite the second row orlevel of bank conta ts, and at the same, time the shaft-controlledcontacts 123 and 124 are closed. The slow acting relay 119 is maintainedin its energized position continuously while impulses are beingtransmitted to the vertical magnet through it, and in its energizedposition closes a circuit extending from ground G through the springs125 and 126 and the relay 128 to battery B. The relay 128, uponenergizing, forms a locking circuit for itself extending from ground Gthrough the springs 104, 105 and 106, springs 107 and 108, springs 129,springs 130 and 131 and the relay 128 to battery B. Thus, upon thedeenergization of the relay 119 after the last impulse is delivered tothe vertical magnet, the relay 128 remains energized and the circuit ofthe rotary magnet 132 is. closed, which circuit extends from ground Grthrough the springs 104, 105 and 106, springs 107 and 108, springs 129,springs 130 and 131, springs 126 and 127, springs 133 and the rotarymagnet 132 to battery B. The rotary magnet 132, upon energizing, rotatesthe shaft 37 the shaft 36 and the wipers 120, 12 1 and 122 one step, andby opening the springs 129 and 133 disconnects ground G from itself andfrom the relay 128. At the same time the shaft-controlled contact 35 isbroken, while the shaftcontrolled contact 135 is closed. If the firsttrunk line of the second level is idle, the relay 128 deenergizes assoon as the springs 129 are opened. If this trunk line is busy, however,the private wiper 121 finds the contact which it engages provided withaguarding ground potential which is transmitted to the relay 128 over acircuit extending from the private wiper 1 21 through the springs 136,springs 130 and 131 and the relay 128 to battery B. This circuitprevents the relay 128 from deenergizing. The rotary magnet 132,however, de'e'nergizes when the springs 133 are opened, regardless ofwhether the relay 128 remains energized or not. If the relay 128 remainsenergized, the circuit of the rotary magnet willbe again closed as soonas its armature drops back far enough to close the-springs 129 and 13The rotary magnet will, therefore, operate in a manner similar to thatof a buzzer to advance the wipers step by step over the contacts untilthe non-grounded contact of an idle trunk line is reached by the wiper121, whereupon the relay 128 deenergizes. The relay 128, upondeenergizing, whether after one or several operations of the rotarymagnet, permanently breaks the circuit of said rotary magnet and closesthe circuit of the switching relay 46. Said circuit is traced fromground G through the springs 104-. 105 and 106, springs 107 and 108,springs 129, springs 130 and 137, 011 normal springs 135, springs 139and 138 and the relay 46 to battery 13. The relay 46, upon energizing,releases the springs shown at 44 in a manner previously explained andopens the springs 170. The springs in the group 44 are so adjusted thatthev make contact with their front contacts before they break contactwith their back contacts. After the springs 44 have operated, a circuitmay be traced from ground G through the springs 104, 105 and 106,springs 107 and 171, springs 140 and 138 and the relay 16 to battery B.After the springs 44 have operated, the ground for the protection of theprivate bank contacts of all the idle selectors in the group of whichthe selector F forms a part is furnished from the round on the privatewiper 121 through the springs 136 and springs 129 to one of theconductors 109. In addition, the operation of the springs 1-1disconnects the line relay 98 from the line and extends the lineconnection over the heavy conductors shown through the wiper 120 and 122to the line relay 57 of the connector H. The line relay 57 thereuponbecomes energized and closes the circuit of the relay 62, which in turn,upon energizing, completes a circuit extending from ground G through thesprings 111, private wiper 121, springs 140 and 13S and the relay 4-6 tobattery B. A branch of the above circuit extends from the private wiper121 through the springs 171 and 107 to the relay 96 of the selector Eand the winding 12 of the line switch C over the circuit previouslytraced. This circuit maintains the relay 46, the relay 96 and thewinding 12 energized after their original energizing circuit is brokenby the deenergization ot the relay 103, which takes place shortly afterits circuit is opened by the relay 46. The deenergization of the relay103 also opens the circuit of the solenoid 38 but not of the solenoid39, as a circuit extends from ground G through the resistance 111,springs 110 and the solenoid 39 to battery B. The solenoid 38, upondeenergizing, disengages the shaft 36 from the shaft 37 and after thepin 40 is removed from the-hole 42, the springs 110 are allowed to breakcontact, thus opening the circuit of the solenoid 39. The solenoid 39,upon deenergizing, removes the guarding ground potential from theprivate bank contacts of all the idle selectors in the group of whichthe selector F is a part, at the same time opening the circuit of therelay 11 1. The relay 111 111 turn, upon deenergizing, closes a releasecircuit from ground G through the springs 116, springs 117 and 142, offnormal springs 124 and the release magnet 143 to battery 13. The releasemagnet 143. upon energizmg, operates to remove the retaining pawls fromthe shaft 37, its own circuit being opened at the springs 12% when saidshal't reaches its lowest position. The control switch I is now inreadiness to be used b another selector switch F (not shown) associatedwith said control switch. and the apparatus used in establishing thiscall is now in readiness to receive impulses tor the third digit 2.

The calling subscriber now operates his calling device for the thirddigit 2 of the called number, whereby the substation impulse springs 6and 7 are separated twice momentarily, each time breaking the circuit ofthe line relay 57 of the connector H. The relay 62 of the connectorbeing slow act ing does not deenergize during the momentaryinterruptions of its circuit by the relay 57, and consequently, eachtime the latter relay de'e'nergizes, an impulse is transmitted over thecircuit extending from ground G through the springs 11% and 115, springs1 16 and 147, relay 63, vertical magnet 50 and the side switch wiper 52(in first position.) to battery I). The vertical magnet receives twoimpulses over this circuit and operates to raise the switch shaft andwipers two steps to a position opposite the second row or level. of bankcontacts, and at the same time the shaft-controlled springs 60 and 61are closed. The slow acting relay 63 is maintained in its energizedposition continuously while, impulses are being transmitted to thevertical magnet through it, and in its energized position closes acircuit extending from ground G through the springs 14S and 14:9 and theprivate magnet 56 to battery This circuit is broken when the relay 63deenergizes after the last impulse has been delivered to the verticalmagnet. The breaking of said circuit causes the private magnet 56 todeenergize, thus permitting the side switch to pass to second position.In passing from first to second posi tion the side switch wiper 52transfers the battery connection from the vertical magnet 50 to therotary magnet 51.

The calling subscriber now operates his calling device for the lastdigit 2, in response to which the connector line relay operates totransmit two impulses through the rotary magnet 51, whereby the shaftwipers are rotated onto the contacts 01 the desired line. The circuit ofthe rotary 11mgnet extends from ground (1 through the springs 11-1 and115, springs 116 and 117, relay 63, springs 151, rotary magnet 51 andthe side switch wiper 52 (in second position) to battery B. The relay 63operates in response to the impulses for this digit in the same manneras for the previous digit to cause the private magnet 56 to advance theside switch to third position. By the engagement ot the side switchwipers 53 and 5 1- with their third-position contact points. the lineconnection completed with the called line. 7 I side switch wiper 55 withits third-position contact point, a circuit is completed through thecut-ofi' winding of the line switch C This circuit extends from ground Gthrough the side switch wiper (in third position) and the cut-offwinding to battery l). The cut-oil? winding of the line switch (l uponenergizing, operates to disconnect the line relay from the calledsuhstation. The connection of ground G with Upon the engagement of thethe connector private bank contact associated with the called lineprevents the called line from being seized by some other connectorswitch. By the engagement of the side switch wiper 52 with its thirdposition contact point, the circuit of the ringer relay 59 is closed.This circuit extends from ground G through the interrupter 153, ringerrelay 59, springs 15st and the side switch wiper 52 (in third position)to battery B. The ringer relay is energized intermittently due to theinterrupter 153 and operates to disconnect the calling line from thecalled line and to bridge the ringing current generator R across thecalled line to signal the called subscriber. Upon the response of thecalled subscriber, his line is provided with talking current through thewindings of the back-bridge relay 58, which relay, upon energizing,closes the circuit through the ringer cut-off relay 155. The saidcircuit extends from ground G through the side switch wiper 55 (in thirdposition), springs '156 and the relay 155 to battery B. The relay 155,upon energizing, interrupts the circuit of the ringer relay at thesprings 154: and closes a locking circuit for itself through the springs157 independent of the springs 156.

Upon the completion of the conversation, the hanging up of the receiverat the calling substation opens the circuit of the line relay 57 of theconnector H. The de'e'nergization of the line relay 57 opens the circuitof the relay 62, which in turn, upon denergizing, opens the holdingcircuit for the relays 16 and 96 and the winding 12, and in additioncloses a circuit from ground G through the sprin 1 1 1 and 1-15, springs14:6 and 158, 0E normal springs 61 and the release magnet 169 to batteryB. The release magnet, upon energizing, removes the retaining pawls fromthe shaft and its own circuit is opened at the springs 61 when the saidshaft reaches its lowest position. The de'e nergization of the relay 46of the second selector F closes a circuit from ground G through thesprings 112 and 159, springs 170, off normal springs 123 and the releasemagnet 160 to battery B. The release magnet, upon energizing, removesthe retaining pawls from the shaft and its own circuit is opened at thesprings 123 when the said shaft reaches its lowest position. Inaddition, the shaft, when in its lowest position, places the springs 1 1again under the control of the relay 16. The deenergization of the relay96 of the first selector E closes a circuit from ground G through thesprings 7 8 and 84:, springs 85,-

said shaft reaches its lowest position. The

deenergization of the holding winding of the line switch C allows theplunger arm 9 to withdraw its plunger from the bank of springs and thusthe line switch is returned to normal.

It having been explained how one subscriber establishes connection andreleases the same, it will now be explained how a connection isprevented from being made with a busy line. If the called number is busythere will be a guarding potential upon the connector private bankcontact associated with that line, just as explained in connection withthe line switch G. The connector private wiper 18, upon engaging thisgrounded contact and before the side switch has passed to thirdposition, completes an energizing circuit through the relay 162. Thiscircuit extends from ground at the private bank contact through theprivate wiper side switch wiper 55 (in second position), springs 163 and16 1, relay 162, springs 165 and 149 and the private magnet 56 tobattery B. The relay 162, upon energizing, opens the circuit of therotary magnet 51 at the springs 151 and connects the busy tone with theline over the following circuit: from ground G through the secondarywinding of the busy machine Q, springs 166, side switch wiper 54k (insecond position) and the condenser 167, thence over the heavy conductorto the calling substation and back over the other heavy conductorthrough the upper winding of the relay 57 to battery B and ground G,thence back to the machine Q. The relay 162, upon energizing, also formsa locking circuit for itself extending from ground G through the oilnormal springs 60, springs 168 and 16l, relay 162, springs 165 and 149and the private magnet 56 to battery 13. The calling subscriber, uponhearing the busy tone, restores his receiver to the switch hook and therelease of the apparatus follows in practically the same manner aspreviously explained.

It will thus be seen that I have devised a very ellicient system inwhich a common switch-operating mechanism is employed for operating aplurality of selector switches, which operating mechanism isautomatically released and reverts to common use as soon as it hasoperated the switch to cut through the connection to the next succeedingswitch.

\Vhilc I have illustrated and described one specific embodiment of myinvention, and have shown the same in connection with automatic switches'of a well-known type, it will, of course, be understood that I do notwish to be limited to the exact form of switches employed, and that,furthermore, this common operating methanisni could be employed inconnection with any form of selector or connector switch.

W hat I claim as my invention is 1. In a telephone system, a pluralityof numerical switches, a common operating shaft normally at rest, andmeans for op eratively connecting any one of said switches with saidshaft and for moving it independently of the others.

2. In a telephone system, a plurality of numerical switches, a commonoperating shaft normally at rest, means for operatively connecting anyone of said switches with said shaft, and means for automaticallydisconnecting said switch from said shaft when said switch has beenoperated.

3. In a telephone system, a plurality of numerical switches, a commonoperating shaft, means for operatively connecting any one of saidswitches with said shaft, and means for preventing two of said switchesbeing connected to said shaftat the same time.

4. In a telephone system, a plurality of subscribers lines, meansincluding selector switches and connector switches for establishingconnection between two of said lines, said selector switches beingdivided into groups, and a common operating mechanism for controllingthe operation of a group of said selector switches one at a time withoutmoving the others, said common mechanism being normally at rest.

5. In a telephone system, a plurality of numerical switches, a commonstep by step operating mechanism for said switches, means for propellingsaid mechanism, and a magnet individual to each switch for controlling acircuit therethrough.

6. In a telephone system, a plurality of numerical switches, a commonstep by step operating shaft, means for operatively connecting any oneof said switches with said shaft, means for propelling said shaft, and amagnet individual to each switch for controlling a circuit therethrough.

7. In a telephone system, a plurality of numerical switches, a commonstep by step operating shaft, means for operatively connecting any oneof said switches with said shaft, means for automatically disconnectingsaid switch from said shaft when said switch has been operated, andmeans for propelling said shaft.

8. In a telephone system, a plurality of subscribers lines, meansincluding line switches, first and second selectors and connectors forestablishing connection between two of said lines, individual operatingmechanism for certain of said switches, common step by step operatingmechanism for other of said switches, and means for propelling saidmechanism to move any one of said other switches independently.

9. In a telephone system, a plurality of subscribers lines, meansincluding selector switches and connector switches for establishingconnection between two of said lines, said selector switches beingdivided into groups, a common step by step operating mechanism forcontrolling the operation of a group of said selector switches, andmeans for propelling said mechanism to move any one of said selectorswitches independently.

10. I11 a telephone system, a plurality of numerical switches, a commonoperating shaft, means for operatively connecting any one of saidswitches with said shaft, means for releasing said shaft afteroperation, and a magnet individual to each of said switches forcontrolling a circuit therethrough.

11. In a telephone system, a plurality of numerical switches, a commonoperating shaft, means for operatively connecting any one of saidswitches with said shaft, means for automatically disconnecting saidswitch from said shaft when said switch has been operated, and means forreleasin said shaft after operation.

12. In a telephone system, a plurality of subscribers lines, meansincluding selector switches and connector switches for establishingconnection between two of said lines, said selector switches beingdivided into groups, a common operating mechanism for controlling theoperation of a group of said selector switches, means for releasing saidmechanism after operation, and a magnet individual to each selector forcontrolling a circuit therethrough.

13. In a telephone system, a longitudinal shaft, a plurality of switchwipers, means for operatively connecting any one of said wipers withsaid shaft, means for releasing said shaft after operation, and a magnetindividual to each wiper for controlling a circuit therethrough.

14. In a telephone system, a longitudinal shaft, a plurality of switchwipers, means for operatively connecting any one of said wipers withsaid shaft, means for automatically disconnecting the selected wiperfrom said shaft when the said shaft has been operated, and means forreleasing said shaft after operation.

15. In a telephone system, subscribers lines, a plurality of numericalswitches accessible to said lines, a common operating shaft, means foroperatively connecting any one of said switches with said shaft, saidcommon shaft controlled from any of said lines, and a magnet individualto each switch for controlling said means.

16. In a telephone system, subscribers lines, a plurality of numericalswitches accessible to said lines, a common operating shaft, means foroperatively connecting any one of said switches with said shaft, meansfor automatically disconnecting said switch from said shaft when saidswitch has been operated, said common shaft controlled from any of saidlines, and a magnet individual to each switch for controlling saidmeans. i

17 In a telephone system, a plurality of subscribers hnes, means moludmgselector swltches and connector switches for establishing connectionbetween two of said lines, said selector switches being divided intogroups, a common operating mechanism for controlling the operation of agroup of said selector switches, said common mechanism controlled overany of said lines, and a magnet individual to each selector forcontrolling the operation thereof.

18. In a telephone system, an automatic trunking switch, a directiveimpulse controlled device temporarily associated with said switchmechanically, trunk lines accessible to said switch, means for operatingsaid device and said switch in synclironism to cause the latter toestablish connection with one 0 said trunk lines, and means for thendissociating said device and said switch whereby said device may bereleased while leaving said switch operated to maintain the connection.

19. In a telephone system, a plurality of lines each line terminatlng inan automatic trunking switch, a plurality of trunk lines accessible tosaid switches, and a device common to all of said lines and operable inresponse to impulses transmitted over any line to direct the movement ofthe trunking switch associated therewith to connect with an idle trunkline.

20. In a telephone system, a plurality of lines, each line terminatingin an automatic trunking switch, a plurality of trunk lines accessibleto said switches, a device common to all of said lines and operable inresponse to impulses transmitted over any line to direct the movement ofthe trunking switch associated therewith to connect with an idle trunkline, and means for restoring said device to normal position after eachoperation while leaving the operated trunking switch and the trunk lineconnected.

21. In a telephone system, a plurality of lines terminating in a pair ofcommon busbars extending to a controlling relay, a trunking switch foreach line, trunk lines accessible to said switches, and a mechanicaldevice under the control of said relay for moving said switches, oneafter the other into connection with idle trunk lines.

22. In a telephone system, a plurality of lines terminating in a pair ofcommon busbars extending to a controlling relay, a trunking switch foreach line, trunk lines accessible to said switches, a mechanical deviceunder the control of said relay for moving said switches, one after theother into connection with idle trunk lines, and means whereby each lineis disconnected from said bus-bars after its associated trunking switchhas been operated.

23. In a telephone system, a plurality of niunerical switches, a commonoperating shaft normally at rest, means for operatively connecting anyone of said switches with said shaft, means for automaticallydisconnecting said switch from said shaft when said switch has beenoperated, and a magnet individual to each switch for controlling saidmeans.

24. In a telephone system, a plurality of numerical switches, a commonoperating shaft, means for operatively connect-ing any one of saidswitches with said shaft, means for preventing two of said switchesbeing connected to said shaft at the same time, and a magnet individualto each switch for controlling said first means.

25. In a telephone system, a plurality of numerical switches, a commonstep by step operating shaft, means for operatively connecting any oneof said switches with said shaft, means for propelling said shaft, and amagnet individual to each switch for controlling said first means.

26. In a telephone system, a longitudinal shaft, a plurality of switchwipers, means for operatively connecting any one of said wipers withsaid shaft, means for releasing said shaft after operation, and a magnetindividual to each switch for controlling said first means.

27. In a telephone system, a dial, a plurality of automatic switches, acommon operating mechanism for said switches, said switches having meansresponsive to a numerical operation of the dial for propelling saidmechanism to cause any one of said switches to elect a group of lines,and a magnet individual to each switch for controlling a circuittherethrough.

28. In a telephone system, a dial, a plu rality of automatic switches, acommon operating shaft for said switches, means for operativelyconnecting any one of said switches with said shaft, said switcheshaving means responsive to a numerical operation of the dial forpropelling said shaft to cause the switch connected therewith to elect agroup of lines, and a magnet individual to each switch for cont-rollinga circuit therethrough.

29. In a telephone system, a dial, a plurality of automatic switches, acommon operating shaft for said switches, electromagnetic means foroperatively connecting any one of said switches with said shaft, saidswitches having electromagnetic means responsive to a numericaloperation of the dial for propelling said shaft to cause the switchconnected therewith to elect a group of lines, and a magnet individualto each switch for controlling a circuit therethrough.

30. In an automatic telephone system, automatic switches of two kindscomprising connecting switches provided with connecting means only andoperating switches pro- Yided with impulse controlled operating meansonly, lines accessible to said connecting switches, means for bringingcertain switches of the first kind separately under the control of anoperating switch, whereby they may be operated to establish connectionsby Way of said lines, and means Whereby after each connecting switch isoperated the said control lSImmSOd and tl1e01 erating switch released.

,Signed by meat Chicago, Cook county, Illinois, this 24th day of August,1914.

ALEXANDER E. KEITH. Witnesses:

GEO; A. YANOGHOWS'KI, HERBERT KRKCKE.

